Have you ever seen a stream flowing in nature? The flowing, always changing water of the stream is what seems to always catch the attention of the viewer. What most people fail to notice is the streambed through which the water flows. As Sebastian Seung stated in his TED talk, this essential indent in the earth shares many qualities with an area of growing interest in the field of neuroscience; the human connectome. The connectome is the bed of the stream floor that guides the neural activity of the human brain. Firstly, the connectome is about structure. This structure includes the links between the neural elements that comprise the human brain; the actual components of the flowing stream. Secondly, the connectome is a map of brain connections; a layout of the stream connections. You may think that this is the same as the first part but the connectivity of the brain goes much further than the structure of the brain. The structure labels the main building blocks of the brain (frontal lobe, parietal lobe, etc.), whereas the map of brain connections will show the connectivity between these brain regions. While it may seem extremely difficult to label all of the connections of the brain down to the smallest neurites, the goal of the connectome is to provide a description of the inner framework that forms the brain on different levels of organization. For example, a connectome shows the inner working of the frontal lobe, while also giving the connections between the frontal lobe and other parts of the brain.
It may be quite a while before one complete human connectome is described. The connectome has been found for the worm C. elegans which has 300 neurons and 7,000 synapses. This process took approximately 10 years from 1970 to 1980 because all of the work was done laboriously without computers. The human brain contains over 100 billion neurons so the number of synaptic connections far exceeds those of the worm.
New types of brain viewing software make it easier for neuroscientists to navigate through a virtual brain, further increasing their knowledge of the connections in the brain. These new 3D maps of the brain will aid in finding more connections between different brain structures in a way that older 2D maps could not. It took 3 years to map the connections of a cube of mouse brain 6 microns on each side. Perhaps this new technology will help decrease the time spent locating these connections. Elsevier’s BrainNavigator 3.0 and the Allen Brain Atlas are two examples of software that is helping pave the way for the connectome. It allows for positioning of a probe or electrode to record activity in any part of the brain, allowing the user to locate the exact path the probe will take. With this software, the task of comparing gene expression data and anatomical information is made very easy. The results can be presented on the screen simultaneously, allowing for visualization of the different brain areas where the genes are expressed. Target genes and 3D views of gene expression are possible as well as the annotation of the slices by scientists for their past experiments. This is a very useful tool in a laboratory because the experimenter can study a 3D layout of the desired slice of the brain before the actual experiment takes place.
To be able to use these online tools requires simple computer skills. To take a trip down your personal stream and find out more about these tools, visit the website of both the BrainNavigator and the Allen Brain Atlas at https://www.brainnav.com/home and http://mouse.brain-map.org/welcome.do respectively.
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